Fifth wheel trailers and tow vehicles for fifth wheel trailers are generally well known in the art. Fifth wheel trailers are much longer, roomier, and heavier than typical tent campers and travel trailers, and thus a fifth wheel trailer typically requires a specially modified, relatively heavy tow vehicle such as a heavy duty pickup truck. The front portion of a fifth wheel trailer extends over the rear portion of the tow vehicle so that a portion of the trailer's weight is carried directly over the rear axle of the tow vehicle. In order to accommodate the weight of the trailer a special hitch assembly is required.
The front portion of the trailer includes a pin box which includes a support plate and a downwardly extending hitch pin. A base plate having an aperture and a latch mechanism is mounted to the tow vehicle, and the support plate carried by the pin box rests on the base plate with the hitch pin secured in the aperture by the latch mechanism. The support plate rotates relative to the base plate with the hitch pin acting as a pivot point. Typically, grease or other lubricant is applied between the support plate and the base plate. The fifth wheel trailer is thus able to pivot relative to the tow vehicle about a vertical axis to facilitate cornering and parking. Normally, the hitch assembly is mounted directly over or a short distance in front of the rear axle of the tow vehicle in order to maintain proper weight distribution.
The vehicle most commonly used to tow fifth wheel trailers is a pickup truck having an 8 foot bed length. On such a truck, there is typically at least 53 inches between the centerline of the rear axle and the rear of the cab. The maximum width for a fifth wheel trailer is 102 inches as dictated by federal highway regulations, which amounts to 51 inches on each side of the pivot point. Thus, in order to prevent contact between the trailer and the cab during cornering, there must be at least 51 inches of clearance between the pivot point and the rear of the cab (sometimes more depending on the fore/aft location of the pivot pin relative to the front of the trailer).
Recently, there has been a consumer trend towards extended cab pickup trucks, which have longer, roomier cabs. These trucks have greatly expanded interior cargo volume and also have specially designed rear jump seats for accommodating additional passengers. Unfortunately, most of these extended cab pickups are built on a standard wheelbase chassis because consumers prefer the driving characteristics of a shorter truck, and accordingly, the bed of these trucks is typically 6 feet long rather than 8 feet long. Although these shorter bed pickups have the towing capacity to handle fifth wheel trailers, they do not have enough clearance between the axle and the rear of the cab to allow the trailer to pivot to 90 degree angle without contacting the cab, which could damage the truck and severely injure any occupants. In most circumstances, a fifth wheel trailer will contact the cab of a short bed pickup at angles much less than 90 degrees.
A number of approaches have been contemplated to adapt fifth wheel trailers to short bed pickup trucks, all of which have their drawbacks. One possible approach is to use a hydraulically operated sliding base to force the hitch assembly, and hence the pivot point, rearward away from the truck cab. Such a system would be expensive, difficult to maintain and would have to be driver actuated. Hence such a system would involve a significant delay or lag time. In an accident such as a jackknife such a system would operate too slowly to prevent the trailer from contacting and most likely damaging the cab.
Another approach, which also uses a sliding base, requires the operator to exit the truck, unlock the base, lock the brakes on the trailer and pull the truck forward. This temporarily moves the pivot point rearward so that the trailer can pivot relative to the truck to a certain extent without contacting the cab. However, before resuming driving, the driver must lock the trailer brakes, back the truck towards the trailer, again exit the truck and lock the sliding hitch, and return to the truck. Obviously, such a system is impractical in many situations, such as negotiating sharp turns in traffic, and is practically useless in an emergency.
Accordingly, there exists a need for an improved sliding hitch assembly that allows fifth wheel trailers to be towed using short bed pickup trucks, but which prevents contact between the trailer and the truck during normal operations. There also exists a need for a sliding hitch assembly that slides automatically in response to pivoting movement between the trailer and the tow truck and that does not require the expense, maintenance and lag time of hydraulic systems, and does not require the operator to exit the vehicle in order to lock or unlock the hitch assembly.